FIG. 1 (Prior Art) is a diagram of a part of the Internet 1. The Internet, loosely defined, is a collection of networks that are interconnected by devices called “routers”. In the illustration, the Internet 1 involves seven networks N1–N7 and five routers R1–R5. A protocol called the Internet Protocol (IP) is used to communicate a message from a source device (a node) on one network to a destination device (a node) on another network. The message is broken up into pieces and each of these pieces is packaged into what is called an “IP packet”. These packets may be of varying lengths. The IP packets of the message are then sent from the source to the destination from one network to the next via the routers. The various IP packets can take different paths to get from the source to the destination. When all the IP packets arrive at the destination, they are reassembled to recreate the original message.
This high level IP message can be transported across an individual network using any one of many lower level protocols. Some of the protocols are packet-based protocols, whereas others of the protocols are cell-based protocols. One packet-based protocol used to transport IP is called Multi-Protocol Label Switching (MPLS). In MPLS, each packet is encapsulated with an MPLS label by the first MPLS device it encounters as it enters an MPLS network. The MPLS device is called an MPLS edge router. The MPLS edge router analyses the contents of the IP header and selects an appropriate MPLS label with which to encapsulate the packet. MPLS packets therefore have varying lengths in the same way that IP packets do. At all the nodes within the network subsequent to the edge router, the MPLS label (and not the IP header) is used to make the forwarding decisions for the packet. Paths through particular nodes in the network are setup from edge to edge, the label defining the particular path its packet will take. Finally, as an MPLS labeled packet leaves the network via an edge router, the edge router removes the MPLS label.
One cell-based lower level protocol used to transport IP over a network is the Asynchronous Transfer Mode (ATM) protocol. In ATM, all packets are of equal length. They are therefore called “cells”. A large IP packet is transported over an ATM network by segmenting the large IP packet into a plurality of smaller pieces. Each of the smaller pieces is packaged to become an ATM cell. The ATM cells are then transported across the ATM network. When the ATM cells reach the edge of the ATM network, their payloads are reassembled to reform the large IP packet. In FIG. 1, networks N1, N5 and N3 are cell-based ATM networks. Networks N2, N6, N4 and N7 are packet-based MPLS networks.
In the example of FIG. 1, networks N3 and N4 are OC-192 high-speed networks adapted to carry traffic over long distances. Router R2 at one end of network N3 may, for example, be located in San Francisco whereas router R4 at the other end of network N3 may be located in New York. Such high-speed long distance networks are often called the “backbone” of the Internet.
In the example of FIG. 1, individual users U1–U10 are coupled to the Internet via local area networks. Networks N1, N2 and N7 are local area networks. In one example where the network is a corporate network serving an office building, the users are corporate employees in a building. In an example where the network is a network operated by an Internet Service Provider (ISP), the users are individual customers that pay the ISP to gain access to the Internet.
Consider the situation where users on networks N1 and N2 issue IP messages that are destined to go to destinations to the right side of the backbone such that the messages should go through one of the two back bone networks N3 and N4. In such a case, the IP traffic from networks N1 and N2 is aggregated and supplied to the router access point on the appropriate backbone network. A portion of the Internet called the “Metropolitan Area” performs this function. In the illustration, the metro area includes a router R1 used for aggregating traffic from networks N1 and N2, and for routing that information to the appropriate one of backbone networks N3 and N4.
FIG. 2 (Prior Art) is a more detailed view of router R1. Router R1 includes line cards 2–3 for interfacing to ATM networks, other line cards 4 and 5 for interfacing to MPLS networks, and a switch fabric 11. ATM line card 3 is coupled to ATM network NS such that router R1 can communicate with backbone network N3 via network N5. Similarly, MPLS line card 5 is coupled to MPLS network N6 such that router R1 can communicate with backbone network N4 via network N6. ATM line card 2 is coupled to ATM network N1 via OC-12 fiber optic link 6, SONET multiplexer 7, higher speed OC-48 fiber optic link 8, and SONET multiplexer 9. MPLS line card 4 is coupled to MPLS network N2 via OC-12 fiber optic link 10, SONET multiplexer 7, higher speed OC-48 fiber optic link 8, and SONET multiplexer 9. SONET multiplexer 7 performs time division multiplexing (TDM) to modulate both ATM traffic from network N1 as well as packet MPLS traffic from network N2 onto the same wavelength channel transmitted over the same fiber optic link 8. SONET multiplexer 9 performs the inverse function of time demultiplexing the signal on fiber optic link 8 to extract and separate the ATM traffic from the MPLS traffic.
Router R1, when it receives an IP message from one of networks N1 or N2, determines whether to forward the message on the message's “next hop” to router R2 or R3. In this way IP network information from the users is aggregated in the metro area and is directed to the correct backbone network for communication across long distances to the destination.
A problem may exist if one of the local area networks coupled to router R1 is disconnected or if the type of traffic on that network is changed from MPLS packet traffic to ATM cell traffic or visa versa. Consider the situation in which ATM network N1 ceases business operations. In that case, the operator of router R1 will likely want to disconnect network N1 from its SONET multiplexer 7 and to couple in the network of another paying customer. For example, the operator may want to disconnect ATM network N1 and to connect in its place MPLS network N7. If this is done, however, MPLS traffic would be received on ATM line card 2. ATM line card 2 is not suitable for coupling to an MPLS network. Consequently, ATM line card 2 may have to be disconnected and a suitable MPLS line card substituted in its place. With the expansion of the Internet and with advances in IP switching technology, it appears that the proportion of packet networks to ATM networks is increasing. Accordingly, as more and more of the networks coupled to a router such as router R1 migrate from one type of traffic to the other, more and more of the line cards of the router will have to replaced. This is undesirable. A solution is desired whereby a smooth and easy migration from one type of traffic to the next is possible without the removal of line cards or the physical manipulation of the router.
FIG. 3 is a diagram of one possible approach to the problem involving a line card 12 that handles both ATM and packet traffic. Line card 12 is coupled to a switch fabric of a router by interface 13. Cell and packet traffic received from fiber optic cable 14 and transmitted on fiber optic cable 15 are time division multiplexed/demultiplexed by TDM device 16. Cell traffic is handled by integrated circuit device 17. Packet traffic is handled by integrated circuit device 18. As the relative amounts of cell traffic to packet traffic change, the same line card can be used.